The present disclosure is generally related to techniques of ensuring bidirectional notification of a unidirectional failure in an optical network and, more specifically, to ensuring protection switching in both directions upon a unidirectional failure in an Optical Transport Network (OTN).
Previously, optical networks had been confined mostly to the so-called long-haul telephone networks which were based upon SONET/SDH technology. The rise of the Internet increased the demand upon these optical networks which were based on less demanding telephonic requirements. To accommodate the transported data, mostly in the form of IP (Internet Packet) packets, protocols were developed for the IP packets to be transported by the SONET/SDH networks, sometimes characterized as POS (Packets over SONET). The adoption of WDM (Wavelength Division Multiplexing) and later DWDM (Dense WDM) technologies increased the capacity of the fibers of the optical network and alleviated some of the pressure of these optical networks. However, the continued increase in the amount of data in IP packets mostly and emerging applications of the Internet, such as voice over IP (VoIP), streaming music, podcasts, IP-based television (IPTV), and high-definition video-on-demand (VoD), has made the POS (Packet over SONET) solution insufficient. Furthermore, the requirements of the new applications often do not easily match the requirements of SONET/SDH technology.
An ongoing effort to move optical networks away from the old telephone-based SONET/SDH technology has been the OTN (Optical Transport Network) which more fully integrates DWDM and IP technologies. The OTN interfaces which are defined by the G.709 standard promulgated by the ITU-T, the Telecommunications Standardization Sector of the International Telecommunications Union, add a “digital wrapper” of OAM&P (Operations, Administration, Management and Provisioning) information to the IP traffic transported over a DWDM network. This additional layer of information enables service providers with the OAM&P capabilities which had been provided by the SONET/SDH transport network. OTN allows IP traffic, such as Ethernet based data, to be transported directly over an OTN without the intercession of SONET/SDH.